Rigging, moving feet affects the main body
So have the feet be controlled by the armature and nothing else? To do that you would have to go to pose mode and right click + shift on the bones that are for the foot, and then right click on that foot. Then press ctrl + p to parent it and click on automatic weights. If you had a single bone for the foot, you could avoid weight paint altogether and just click bone instead of automatic weights. I am not very good at weight painting so not gonna talk about that.

Also, currently the feet are a single model I think? If you are using the mirror modifier like I think you are, then apply it and then go to edit mode with tab. Then press p and click by loose parts. this will separate the feet into separate models which you can then select once you have left edit mode. To make these easier to move, you should probably go to object - transform - origin to geometry from the little pop out menu near the bottom of the screen.